Source Driven Rotating Flow in a Basin with Topography

Laboratory experiments on a rotating tank of fluid are used to study the fundamental aspects of geophysical fluid flows. The present set of experiments are an attempt to study the effect of a rectangular ridge on the flow of a rotating fluid confined by lateral boundaries and forced by a source. First dye and later Particle Image Velocimetry (PIV) are used to understand the circulation in the domain. A strong southern boundary flow near the western wall of the domain and a cyclonic circulation in the trench are observed in these experiments. Overflow from the eastern side to the west of the ridge is seen along the N-S length of the ridge, though the overflow is pronounced near the northern boundary of the domain. Simplified mathematical models are used to describe the observed circulation. Numerical simulations are conducted using the MIT general circulation model on a large scale idealized box domain with a topography similar to the one we used in the laboratory tank as well as a rectangular trench parallel to the eastern wall of the domain. A point mass source contributes to the upwelling at the free surface. This set up represents a homogeneous abyssal layer upwelling slowly due to a polar source. Results indicate a cyclonic sense of circulation and a poleward eastern boundary current over the ridge wall. This intensification can be attributed to the vortex stretching over the slopes of the ridge, as the vertical walls appear in the numerical model as having a steep slope. Friction on vertical walls of the ridge are also a cause of this intensification. Some features of the observed and modeled circulation are compared to the oceanic flow in the deep Pacific Ocean.